Fix is from OpenBSD ffs_softdep.c v1.79, originally from FreeBSD
ffs_softdep.c 1.196. Commit message from OpenBSD:

"due to ffs_sync not be able to sync some buffers here is another
instance of softdep code that must ensure proper syncing.
try harder to flush MKDIR_BODY dependancy if such still exists
during pagedep flush (that is by syncing first block of the dir)."